The present invention is directed to a pump for supplying liquid to a source and is particularly directed to, but not limited to, a fuel pump for supplying fuel for use in an internal combustion engine. The fuel pump is applicable for use with a fuel injection system used in motorcycle engines and the present invention will be described with reference to this application. It is to be appreciated that the pump is also applicable for use in other applications, particularly where priming of the pump is a concern.
Fuel injection systems for internal combustion engines typically require a fuel pump to supply fuel to the fuel and/or delivery injectors of the injection system. When the fuel supply to the fuel pump is interrupted and the remaining fuel in the pump is pumped out, it is necessary to re-prime the fuel pump. Typically, it can take a number of seconds to re-prime a fuel pump because of the presence of air and/or fuel vapour upstream of and within the fuel pump. Generally, this gas must be removed before the fuel pump can operate properly.
A similar problem also exists when the fuel to be delivered by the fuel pump is at a high temperature in a fuel tank, from which fuel is supplied to the fuel pump. At such significantly high temperatures, vapour typically forms and may constitute a significant amount of the fuel volume presented to the fuel pump. This problem is commonly known as xe2x80x9chot fuel handlingxe2x80x9d and for the fuel pump to operate properly this fuel vapour or gas must also be removed, from the vicinity of the fuel pump.
One way of removing such gas or vapour present upstream from or within the fuel pump is by pumping the gas downstream of the fuel pump, the gas, for example, being subsequently returned to the fuel tank by a fuel regulator. In this scenario it is however difficult for the fuel pump to pump a compressible gas or vapour as it may tend to simply compress and expand within the pump without being displaced therefrom. This results in a significant period of time being taken to displace the gas from the pump before fuel can be supplied to the fuel injection system. Further, in such pumps it may be difficult to achieve a sufficient compression ratio to pump air against a significant back-pressure downstream of the pump. Such a back-pressure may, for example, be presented by a downstream pressure regulator. In particular regard to the Applicant""s dual fluid fuel injection system such as that disclosed in U.S. Pat. No. 4,934,329, the contents of which are incorporated herein by reference, this problem may be more prevalent in that it may present an absolute downstream pressure in the range of 750 kPa, whereas a conventional manifold injection system may present a pressure of only 380 kPa, or thereabouts.
One possible solution is the use of a pump having a higher compression ratio which will more effectively facilitate the pumping of gas or vapour downstream of the fuel pump. However, in regard to simple, low cost fuel systems and/or engine applications, this in itself poses a problem from the point of view of achieving a desired low-cost manufacture of the fuel pump. An additional problem is that the power requirements of commercial pumps having the required high compression ratio are generally too high for simple low cost engine applications such as motorcycle or scooter applications.
It is therefore an object of the present invention to provide a pump, and in particular a fuel pump which can be re-primed after an interruption in, or the exhaustion of, the supply of fuel thereto within a shorter period of time than for known fuel pumps, particularly where comparatively high pressures are to be developed.
It is a further object of the present invention to provide a pump and in particular a fuel pump, which has good hot fuel handling capabilities.
With this in mind, there is provided a pump, for pumping fluid including:
a pump body having a pumping chamber therein;
an inlet control means adapted to be in fluid communication with a fluid supply means for supplying fluid to the pump;
and an outlet control means adapted to control the delivery of fluid from the pump;
wherein
when a fluid at least substantially consisting of gas or vapour is supplied to the pumping chamber through the inlet control means, the fluid is pumped upstream from the inlet control means,
and when a fluid at least substantially consisting of liquid is supplied to the pumping chamber through the inlet control means, the fluid is at least substantially pumped through the outlet control means.
Preferably, the pump is a fuel pump arranged to receive fuel from a fuel supply means and to pump fuel through the outlet control means. Further the pump has good xe2x80x9chot fuel handlingxe2x80x9d capability in that it has the capacity to reject vapour continuously during steady state operation.
The pump according to the present invention is designed to not pump gas, typically in the form of air or vapour, downstream of the pump when such gas is presented to the inlet control means as a significant component of the fluid to be pumped. Any such fluid comprising a significant gas component which enters the pump is instead made to pass back through the inlet control means towards the fluid or fuel supply means. As will be alluded to hereinafter, the gas component within the fluid which enters the pumping chamber is gradually reduced until the gas no longer forms a significant component of the fluid. This point is achieved when the effective compression ratio within the pumping chamber is sufficient to overcome the back-pressure downstream of the outlet control means. At this point in time, the fluid within the pumping chamber will be pumped through the outlet control means. The fluid will be substantially liquid, but under certain conditions may still comprise a small component of gas therein, typically 5% by volume or less.
The pump according to the present invention is therefore effectively self priming and separates any gas from the fluid such that at least substantially only liquid is pumped through the outlet control means. This results in faster re-priming times for the pump, and when applied to fuel pumps for internal combustion engines, allows a high enough effective compression ratio, due to liquid rather than air being in the pumping chamber, which allows pumping against a high back-pressure downstream of the pump.
The inlet control means may include an inlet control member for controlling the flow of fuel and/or gas to and from the pumping chamber. The inlet control member may be accommodated within an inlet bore having an inlet port at one end thereof, and an end stop face at an opposing end thereof. The inlet control member may be freely moveable within the inlet bore between the inlet port and the end stop face of the bore. At least one inlet discharge passage may extend between the end stop face of the inlet bore and the pumping chamber to allow the flow of fluid to and from the inlet bore and the pumping chamber. The discharge passage(s) may be offset relative to the central position of the inlet control member such that fluid flow though the passage(s) may still occur when the inlet control member abuts the end stop face.
The inlet control member may be spherical in shape and the inlet port may be provided with a valve seat upon which the inlet control member can abut to close off the inlet port preventing fluid flow through the inlet bore. It is however to be appreciated that alternative shapes of the inlet control member are also envisaged. For example, the inlet control member may alternatively be disc shaped.
A predetermined clearance may be provided between the internal walls of the inlet bore and the inlet control member. Further, a predetermined axial travel or xe2x80x9cstrokexe2x80x9d for the inlet control member within the inlet bore may also be provided. The clearance and the stroke may be a function of the diameter of the inlet control member, this function allowing the inlet control means to operate according to the present invention. According to one preferred embodiment, the diametrical clearance is equal to one tenth the diameter of the inlet control member.
An inlet filter screen may be provided within an inlet duct of the inlet control means upstream of the inlet port and downstream of the fuel supply means.
The pump may further include a fluid discharge means for delivering fluid which is pumped through the outlet control means to a desired source. The outlet control means may include a check valve means responsive to the pressure in the pumping chamber for controlling the flow of fluid from the pumping chamber.
The pump may include a piston located within the pumping chamber. The piston may be actuated by an eccentrically mounted cam. A bearing means may be provided about the cam for engaging one end of the piston. The bearing means may, for example, be provided in the form of a sleeve bearing on a follower supported on or integral with the piston. The eccentric cam may be driven by an electric motor. Alternatively, the piston may be actuated by a linear actuator responsive to engine operating variables.
As compared to a conventional roller cell type fuel pump, the above described arrangement utilises an electric pump having lower power requirements due to the lower pump leakage between high and low pressure regions in the pump. This allows a fuel pump according to the present invention to be used more effectively on motor-scooters and other small engine applications.
Where the pump is a fuel pump, the fluid supply means may be a fuel reservoir, and an upstream supply line may connect the inlet control means via the inlet duct to the fuel reservoir. The upstream supply line may be directly submerged within the fuel reservoir or may be comprised by a hose connected to a fuel reservoir located directly above the fuel pump. Preferably, the fuel pump may be entirely submerged within the fuel reservoir and may draw fuel from the upstream fuel supply line. The fuel pump may then subsequently deliver high pressure fuel via the fluid discharge means to a downstream fuel supply circuit located externally of the fuel reservoir.
Depending on the position of the inlet control member within the inlet bore, the inlet port will be selectively closed off or will be opened to allow fuel and gas to pass through the inlet port and through the inlet discharge passage(s) to the pumping chamber. The axial travel, mass and diameter of the inlet control member, together with the clearance in the containing inlet bore, define the selected response of the inlet control member relative to the selected fluid velocities developed as a result of the pressure and volumetric conditions in the pumping chamber.
As a result, fluids with a lower average specific gravity and viscosity, such as fuel containing air or vapour, are ejected at high velocity upstream of the fuel pump past the inlet control member, the inlet port and the inlet filter screen. The velocity of the fluid pumped through the inlet control means is dependent upon the amount of gas compared to liquid that there is in the fluid. Generally, as the component of gas within the fluid is gradually reduced, the fluid is pumped past the inlet control member with greater velocity. The velocities of the fluid are typically sufficient to overcome the surface tension on the surface of the inlet filter screen which would normally prevent air or vapour from passing in the direction away from the pumping chamber due to buoyancy forces alone.
The axial proximity of the inlet filter screen relative to the inlet port, on the one hand, and the bore size of the inlet port, on the other hand, are selected in relation to the displaced volume per stroke in the pumping chamber during one cycle in order to provide the minimum required velocity of ejection through the inlet port so as to ensure that air and vapour pass through the inlet filter screen in the upstream direction. Thereby, entrained air and vapour are ejected into a low-velocity region of the inlet duct such that buoyancy and bubble coalescence forces may act to remove such air and vapour from the inlet duct. Such vapours and gases may pass back to the fuel within the fuel reservoir due to the buoyancy forces and the lack of velocity of the fuel in the downstream direction within the inlet duct, such velocity being selected by the diameter of the inlet duct relative to the average rate of liquid pumping provided by the motor and pumping chamber during normal steady-state operation.
Conversely to the above, when fluids without a significant percentage of entrained air or fuel vapour are drawn in to the pumping chamber of the fuel pump, the effective compression ratio within the pumping chamber is sufficient to overcome the check valve means of the outlet control means and the back-pressure downstream of the outlet control means. Hence, when predominantly liquid is present in the pumping chamber, the pump is able to effectively pump this liquid, typically fuel, to the fluid discharge means via the outlet control means.
The actual behaviour of the inlet control member within the inlet bore as noted above is a function of the specific gravity and viscosity of the fluid passing through the inlet control means relative to the cyclic volume flow conditions created by the pumping chamber. During operation of the fuel pump, and particularly when fluid which is substantially gaseous by volume is present in the pumping chamber, the inlet control member xe2x80x9coscillatesxe2x80x9d within the inlet bore due to the periodic changes in the direction of fluid flow through the inlet bore. The phase and amplitude of this oscillation varies as a function of the specific gravity and viscosity of the fluid passing around the inlet control member. This periodic change of direction of fluid flow is due to the piston moving through its pumping and return strokes and hence cyclically changing the volume and pressure within the pumping chamber.
When the fluid within the pumping chamber is at least substantially gas, the oscillation of the inlet control member is substantially xe2x80x9cout of phasexe2x80x9d with the frequency of the direction change of the fluid passing through the inlet bore. The net result is that the check valve of the outlet control means stays closed and gas/vapour entrained in liquid passes in and out of the pumping chamber, past the control member and the inlet port. As the gas and/or vapour which are entrained in the liquid are forced back and forth between the pumping chamber and the upstream inlet duct, some of the vapour or gas is sufficiently removed to a point upstream of the inlet port such that it may coalesce into bubbles large enough to rise by buoyancy forces against the relatively low downstream fluid velocity in the inlet duct. This gas or vapour is replaced by liquid in the pumping chamber and the inlet bore. Accordingly, gas or vapour present in the fluid is effectively separated from the relatively high velocity fluid in the pumping chamber and the inlet bore. This continues to happen until the component of gas by volume within the fluid in the pumping chamber is reduced to a point where it is no longer significant such that the amount of liquid in the pumping chamber eventually becomes sufficient to allow the effective compression ratio for pumping through the outlet control means to occur.
Whilst this priming phase of operation is occurring, the phase of oscillation of the inlet control member varies progressively closer to the phase of fluid movement as the average specific gravity and viscosity of the fluid increases. When the fluid is at least substantially liquid, the movement of the inlet control member generally moves in phase with the fluid flow through the discharge passage(s) such that the inlet port is selectively blocked by the inlet control member. The fluid is therefore prevented from returning to the inlet duct and fuel reservoir and is instead able to displace the check valve of the outlet control means and be pumped downstream from the pump. Since the effective compression ratio within the pumping chamber is such that pumping through the outlet control means can occur whilst there is still a small component of gas within the fluid in the pumping chamber, the pump may, under certain circumstances, deliver this small component of gas with the liquid through the outlet control means. However, under most circumstances, the fluid will generally be primed of all gas by the operation of the pump such that only liquid fuel will be delivered thereby.
It will be convenient to further describe the invention by reference to the accompanying drawings which illustrates one possible arrangement of a fuel pump according to the present invention. Other arrangements of the invention are possible, and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.